1. Field of the Invention
This invention relates to a method and apparatus for shrinking plastic film around an article or a group of articles.
2. Description of the Prior Art
The use of biaxially or preferentially oriented plastic film capable of being heat shrunk has found wide application in packaging articles and groups of articles. Many apparatuses and processes are currently in use in the marketplace for wrapping articles in both uniaxially oriented and biaxially oriented plastic film. These apparatuses use film in the form of endless sheets which are cut into panels and wrapped around articles or groups of articles and also utilize performed bags which are placed over groups of articles. One area which has experienced exceptionally fast growth in the last few years is the area of pallet packaging using preformed heat shrinkable bags or sheets of plastic to surround the articles carried on a conventional pallet which can be handled by a forklift truck. At present there are generally two systems utilized for shrink wrapping palleted articles in shrink film. One system utilizes a heat tunnel wherein the palleted articles are encased either in a preformed plastic bag or are wrapped with sheets of oriented plastic and then passed through a heat tunnel where the temperature is rapidly raised to cause the plastic film surrounding the pallet to shrink tightly to the articles on the pallet and the base of the pallet itself. The second form of apparatus used is where the pallet is placed on a base, or either set on the floor, and the articles are covered by either a plastic preformed bag or by sheets of plastic material, and a heating device is passed down over or around the palleted products encased in the plastic bag, and heat is applied from the heating device to the plastic to cause it to shrink about the articles carried on the pallet. Some of these machines are relatively simple and do not require the extensive investment as do the heat tunnel type shrinking installations.
However, one of the shortcomings of the single pallet, stationary, shrink apparatuses is found in their heat application assemblies. Most of the pallet shrink apparatuses equipped with a moving heat source now utilize either open gas flames, electrical resistance heaters of the calrod type, banks of quartz heating elements, or banks of heat lamps. The prior art devices have experienced considerable difficulty in achieving a uniform heat application whereby an even and controlled shrinkage of the plastic wrap about the palleted articles occurs. Open flame shrink devices have the disadvantage that the flames are difficult to control and cannot be used in a hazardous atmosphere. Additionally, they cause burn spots and overheating of the plastic wrap on occasions. Electrical powered heaters suffer deficiencies in that they do not provide a high efficiency for the power utilized. All of the foregoing methods of applying heat to shrink film palleted articles are rather slow and involve excessive use of the energy sources such as gas or electricity.
Thus, there is a need in the field of shrink wrapping palleted articles to provide a method and apparatus which can rapidly and economically shrink a plastic film around a group of palleted articles.